The present invention relates to a data processing apparatus for reading data stored in a memory of a data carrier by a communication due to a contactless coupling by a reader/writer and for processing the data. More particularly, the invention relates to a data processing apparatus using a reader/writer and data carriers, in which when a plurality of data carriers simultaneously access to one reader/writer, data is read out from each of the data carriers and the data is eventually read out from all of the data carriers.
Hitherto, as such a type of data processing apparatus, for example, there is an apparatus shown in FIG. 1. In FIG. 1, a reader/writer 100 comprises: a control section 102; a reading section 106; a data return command section 104; a transmitting section 108; and a decoding section 110. A data carrier 200 comprises: a control section 202; a memory 206; a modulating section 208; and a transmitting section 204. When performing a reading operation from the reader/writer 100 to the data carrier 200, a read command is transmitted by the reading section 106. The read command is constructed by, for example, [(a read command)+(a read start address)] or the like. The data carrier 200 which received such a command sets the memory 206 into a reading state and also sets an address or the like as necessary. The reader/writer 100 subsequently transmits a data return command. The data carrier 200 which received such a command reads out the data from the memory 206 on a unit basis of a specified number of bits and converts the data to a transmission signal by the modulating section 208 and transmits the signal by the transmitting section 204. The reader/writer 100 receives the signal from the data carrier 200 and decodes data by the decoding section 110. The apparatus repeats the above processes a number of times as many as the number of bits of the data to be read out, thereby reading out target data as a result. In such a conventional data processing apparatus, however, there is a problem such that when two or more data carriers 200 simultaneously access to the reader/writer 100, the data cannot be correctly read out.